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/*
* syscall_nt.c - checks syscalls with NT set
* Copyright (c) 2014-2015 Andrew Lutomirski
*
* This program is free software; you can redistribute it and/or modify
* it under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* Some obscure user-space code requires the ability to make system calls
* with FLAGS.NT set. Make sure it works.
*/
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <asm/processor-flags.h>
#ifdef __x86_64__
# define WIDTH "q"
#else
# define WIDTH "l"
#endif
static unsigned long get_eflags(void)
{
unsigned long eflags;
asm volatile ("pushf" WIDTH "\n\tpop" WIDTH " %0" : "=rm" (eflags));
return eflags;
}
static void set_eflags(unsigned long eflags)
{
asm volatile ("push" WIDTH " %0\n\tpopf" WIDTH
: : "rm" (eflags) : "flags");
}
int main()
{
printf("[RUN]\tSet NT and issue a syscall\n");
set_eflags(get_eflags() | X86_EFLAGS_NT);
syscall(SYS_getpid);
if (get_eflags() & X86_EFLAGS_NT) {
printf("[OK]\tThe syscall worked and NT is still set\n");
return 0;
} else {
printf("[FAIL]\tThe syscall worked but NT was cleared\n");
return 1;
}
}
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